Electrical apparatus



May 27, 1958 H. F. CLARK 2,836,781

ELECTRICAL APPARATUS Filed April 8, 1957 Insular/on INVENTOR, Harry F. Clark His Afro! nay United States Patent O ELECTRICAL APPARATUS Harry F. Clark, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application April 8, 1957, Serial No. 651,322

3 Claims. (Cl. 318-421) This invention relates to, electrical apparatus and more particularly to inexpensive electromagnetic starting controls for small split-phase motors.

It is diflicult to build inexpensive electromagnetic starting relays for small split-phase motors for operation over a wide range of supply voltages. The difiiculty resides in the fact that the difference between the main winding current at starting and the current balance speed is barely adequate to provide satisfactory pull-in and drop-out of the relay at normal voltages. It is quite insufficient at low voltages, so that the relay fails to operate satisfactorily when abnormally low voltages are encountered.

It is an object of this invention to increase the difference between the current through the electromagnet relay coil at the start and at balance speed so that the relay will operate properly over a wide range of voltages.

These and other objects are attained in the arrangement shown in the drawing in which a small temperature responsive resistance is placed in series with both winding circuits adjacent the relay and a shunt provided with a small resistance is placed around the small resistance and the operating coil of the relay. A 50% increase in resistance of the small resistance during the starting period will increase the diifercnce between the current flow through the operating coil of the relay between starting and balance speeds from about 25% in a conventional arrangement to about 50% in the arrangement disclosed and claimed herein.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

In the drawings:

Figure 1 is a view of a motor control embodying one form of my invention; and

Figure 2 is a. simplified wiring diagram of the motor and motor control shown in Fig. 1.

Referring now more particularly to Fig. 1, the supply conductor L connects through a control switch 20 and a conductor 22 to the stationary overload contact 24.

- This contact 24 is normally engaged by the contact on the overload cantilever bimetal 26 anchored to the reversed L-shaped metal support 28 staked edgewise to the base 30 of electrical insulating material. The free end of the bimetal 26 is connected by a G-shaped toggle spring 32 to the hook-shaped free end of the compensating overload bimetal 34 which is anchored to the long part of the metal support 28.

The supply conductor L connects to the junction of the main winding 36 and the phase winding 38 of the motor 44). The phase-winding 38 is connected by conductor 42 to the stationary starting contact 44 fixed to the base 30. The main winding 56 is connected by the conductor 46 to the terminal 48, in turn connected to one terminal of the electromagnet coil 50 which is wrapped around the otfset portion of the flat bar core 52 of magnetic material. The lower end ol' the bar core 52 is provided with a wire or fiat hinge spring 54 connecting with the lower end of the flat bar armature 56. This armature 56 carries a lead weight 58 and a felt pad 64} to prevent chattering.

The lower end of the core 52 also supports a support member 62 which supports the lower end of a cantilever spring contact blade 64 having an offset portion 66 carrying a contact adapted to engage the stationary contact terminal as. T he spring contact blade 64 has a projection 68 extending upwardly from the offset portion 66 which is held by the stop 70 of a non-ferrous metal fastened to the top of the core 52 to limit the movement of the blade 64 away from the stationary contact 44. The blade 64 has an inherent spring force tending to cause it to bow to the left, while the spring hinge 54 has an inherent spring force tending to carry the armature bar 56 to the right. This balancing of one spring force against the other provides a simple, inexpensive way of making the relay sensitive and also prevents chattering of the con tacts by reason of the fact that the attraction of the electromagnet coil 50 holds the armature 56 away from the projection 63, thus allowing the blade 64 to continuously engage the contact 44 and be continuously disengaged from the armature 56.

With a typical /8 H. P. split-phase motor, the main winding current upon 125 volts supply voltage will drop from 10 amps, at the start to 6 amps. at balance speed. This is a drop of about 40%. At 115 volts the main winding current drops from 9 amps. at the start to 5.7 amps. at balance speed, a drop of about 35%. However, when the voltage falls to 90 volts, the main winding current at the start is 6 amps. while at balance speed the current falls only to 4.8 amps. This drop at 90 volts is, therefore, only about 20%, which is insufiicient to cause proper pull-in and drop-out of even a relatively sensitive relay such as is shown herein.

According to this invention, the second end of the main winding coil 52 connects to a junction 72 of a conductor 74 connecting with the contact blade 64 through the core 52 and the extension 62 and a conductor 76 connecting through a small positive temperature responsive resistance 78 connecting with the member 28. In addition to this, there is a larger resistance 80 connected between the member 28 and the terminal 48 in shunt with both the resistance 78 and the operating coil 50 of the electromagnet.

The resistance 78 is preferably of very fine temperature responsive resistance wire having a value of about .02 of an ohm but will increase rapidly upon current flow to .03 of an ohm. For example, this resistance may be made of tightly coiled, fine copper or nickel wire. The resistance 80 may, for example, have a value of .02 of an ohm. If desired, the resistance 80 may have a negative temperature coefiicient of resistance. Also, if desired, if the resistance 80 has a very sensitive and very rapid decrease in resistance with increasing temperatures, the resistance 78 could be a normal resistance of .02 ohm.

With this arrangement, the current through the electromagnet coil 50 at 125 volts is 7.7 while at balance speed it falls to 3.1. At 115 volts, the current flow through the coil 59 is 6.9 amps. and at balance speed is 3 amps. At volts the current flow through the coil St) at the start is 4.6 amps. and at balance speed it fails to 2.6 amps. This is a decrease of about 42%, which insures satisfactory operation of the relay not only at 90 volts but at even lower voltages. The relay will operate satisfactorily if set to pull in or close at 4.6 amps. and to drop out or open at 3.1 amps. Thus, by this new arrangement I am able to cause the relay to operate satisfactorily over a much wider range of voltages so that the motor will start under wide variations in supply voltages.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, as may come within the scope of the claims which follow.

What is claimed isas follows:

1. A control for an electric motor having main and phase windings and supply conductors, an electromagnetic starting relay having its contacts connecting one of the supply conductors and one terminal of the phase winding and having its operating coil connecting one of the supply conductors and one terminal of the main winding, the second supply conductor being connected to the second terminals of the main and phase windings, a small resistance connected in series with both the main and phase windings between said operating coil and said one supply conductor, and a higher resistance connected in shunt with both said small resistance and said operating coil.

2. A control for an electric motor having main and phase windings and supply conductors, an electromagnetic starting relay having its contacts connecting one of the supply conductors and one terminal of the phase winding and having its operating coil connecting one of the supply conductors and one terminal of the main winding, the second supply conductor being connected to the second terminals of the main and phase windings, a

small resistance connected in series with both the main and phase windings between said operating coil and said one supply conductor, and a higher resistance connected in shunt with both said small resistance and said operating coil, said small resistance being composed of temperature responsive material having positive temperature responsive resistance characteristics providing increasing resistance with increasing temperatures.

3. A control for an electric motor having main and phase windings and supply conductors, an electromagnetic starting relay having its contacts connecting one of the supply conductors and one terminal of the main winding and having its operating coil connecting one of the supply conductors and one terminal of the phase winding, the second supply conductor being connected to the second terminals of the main and phase windings, a small resistance connected in series with both the main and phase windings between said operating coil and said one supply conductor, and a higher resistance connected in shunt with both said small resistance and said operating coil, one of said resistances being composed of temperature responsive material for reducing the current flow through said operating coil during the starting period.

No references cited. 

